1. Field of the Invention
The invention relates to methods for fabricating an IBIIIAVIA-group amorphous compound, and more particularly to methods for fabricating an IBIIIAVIA-group amorphous precursor used for a thin-film solar cell.
2. Description of the Related Art
Thin film solar cells have already been researched and developed, as countries search for available and clean energy. For electric power, power generator systems mainly comprise thermal power, waterpower, and nuclear power generators. However, the thermal power generator uses fossil fuels that cause environmental pollution problems such as air pollution, acid rain, greenhouse effect, etc. In addition, fossil fuels have limited supply. for waterpower, waterpower generators are not very practicable due to geographic limitations. For nuclear power generation, nuclear waste generated therefrom, seriously and negatively impacts the environment. Therefore, an energy source, which is not a pollutant and is highly practicable and unfailingly available, is desired. At present, the most potential energy power is solar power energy as it is inexhaustible, safe for the environment, and not limited to geography. In other words, solar power energy is a clean and practicable regenerated power source.
For thin film solar cell research, a major objective is to manufacture a device with a low cost and a simple manufacturing process for mass production. The thin film solar cell can be classified, according to material, such as an amorphous silicon, CdTe, and CIGS (CuInGaSe) thin film solar cell. The CIGS thin film solar cell with CIGS material using a light-absorbing layer has superior conversion efficiency 19.9% versus other materials. In addition, the CIGS thin film solar cell has advantages of, composition transformation, variable band gap and ability for transformation into p-n type semiconductors. Also CIGS thin film solar cells have the most optimum absorption coefficient amount direct band gap semiconductor materials. Moreover, the CIGS thin film solar cell is reliable as it does not have Staebler Wronski effect as do amorphous silicon materials and poisonous cadmium as do cadmium telluride materials. Therefore, CIGS materials are desired for use in thin film solar cell.
The CIGS light-absorbing layer of the thin film solar cells is usually formed by an electro-deposition, spray pyrolysis, sputtering, co-evaporation, etc. process. The impurity in the CIGS light-absorbing layer affects the conversion efficiency of the thin film solar cell. Thus, the Cu(In, Ga)Se2 material is usually formed at a high vacuum (10-4 torr˜10-7 torr) to avoid external impurities and improve film quality. However, since the cost for vacuum manufacturing is higher than non-vacuum manufacturing, a non-vacuum manufacturing procedure is desired.
At present, powders used for the wet coating method is formed by conventional methods such as a solid state method, a hydrothermal/solvothermal method, a sol-gel method, a polyol reduction method, etc. For example, Bhattacharya et al. (U.S. Pat. No. 5,731,031) manufactures a crystal powder precursor for solar cells, such as CuxSen (x=1-2, n=1-3), CuxGaySen (x=1-2, y=0-1, n=1-3), CuxInySen (x=1-2.27, y=0.72-2, n=1-3), Cux(InGa)ySen (x=1-2.17, y=0.96-2, n=1-3) and InySen (y=1-2.3, n=1-3), by the chemical bath method. However, at present, the powders used for the wet coating method are crystalline. Thus, it is difficult to precisely control the composition and particle size of the crystalline powers. Therefore, an improved method for easier control of the composition and particle size of the crystalline powers is desirable.